Traditional motor starter circuits are provided with a thermal circuit breaker, which is also called thermal switch or winding protection switch. In induction motors for compressors for domestic appliances or heat pumps for air-conditioning systems, the thermal switch can be located in a hermetically closed compressor housing. The thermal switch or winding protection switch is usually closed and serves the purpose of interrupting the current flow through the auxiliary winding and the main winding, if the rotor seizes and the power exceeds a permissible maximum value or too much heat is released in the winding. As general state of the art the documents DE 197 35 552 A1, EP 0 924 735 A3, U.S. Pat. No. 5,818,122 and JP 58107069 A are mentioned, which disclose different safety elements or safety switches for current circuits in vehicles, said elements or switches being connected to a vehicle battery.